Under the 3GPP standards, a NodeB (or an eNB in LTE (i.e. Long Term Evolution)) is the base station via which mobile devices connect to the core network and which defines a cell of the network. Home base stations (HNB) provide short range 3G radiofrequency (RF) coverage, and are sometimes referred to as a femto access point (FAP). Where the home base station is operating in accordance with the LTE standards, the HNB is commonly referred to as an HeNB. Some base stations, sometimes referred to as HNB/HeNB, can operate in accordance with both the 3G and LTE standards, and therefore define a dual mode femtocell. The HNB/HeNB base station may also sometimes be referred to as a dual femto access point (FAP).
The HNB or HeNB provides radio coverage (for example, 3G, 4G and/or WiMAX) within the home, small or medium enterprise, shopping malls, etc. and typically connects to the core network via a suitable residential gateway RG and public or corporate broadband (BB) access network (for example via an ADSL link to the Internet). The HNB or HeNB is given an IP address by the local network to which it is connected, and the HNB or HeNB provides this IP address to the mobile telephone operator network so that it can reserve appropriate resources for the HNB or HeNB through the broadband access network.
During operation in a normal operation mode or normal state, the HNB or HeNB enables users of a User Equipment (UE) to communicate with other such users via one of a number of the base stations (eNodeB, eNB) and a core network.
In a connected or active state or mode, a UE is registered with the network and has an RRC (Radio Resource Control) connection with a base station, so that the network can identify which cell the UE belongs to and can transmit data to and receive data from the UE. In LTE, in the active state or mode, the Handover procedure allows UEs to have service continuity whilst moving within the Intra LTE system (Intra RAT and Inter Frequency) and towards other RATS (Radio Access Technologies).
A UE also has a power conservation or idle state or mode in which, typically, the UE is not transmitting or receiving data, and no context about the UE is stored by the base station. In the idle state, the location of the UE is known only (to the MME (Mobility Management Entity) in 3GPP) at the granularity of a Tracking Area (TA) comprising a cluster or group of base station cells. When in the idle state, a UE selects and reselects cells according to the parameters broadcast by the base station in the BCH (Broadcast Channel), with a frequency given by a Tracking Area Update Timer Value, and the base station is not aware of the cell selections/reselections made by the UE.
During the normal operation mode, the HNB or HeNB usually periodically broadcasts a downlink transmission comprising reference signals and system information, for instance both the Pilot and the Broadcast Channels, to signal its presence to UEs.
This broadcast by the HNB or HeNB consumes a relatively significant amount of energy and also results in human exposure to radiation. If there is no UE in the coverage range of a HNB or HeNB, this broadcast may be seen as an unnecessary waste of energy and an unnecessary human exposure to radiation. Additionally, the HNB or HeNB, by continuously transmitting the Pilot and Broadcast Channels, may cause interference with a neighbouring HNB or HeNB.
In order to mitigate these drawbacks, a HNB or a HeNB can enter an energy saving mode or state in which the amount of energy consumption by the HNBs or HeNBs, as well as the human exposure to radiation and interference caused to neighbouring HNB or HeNB, are reduced.
To this end, in the normal operation mode, each HNB or HeNB checks if there are any UEs in the idle or connected state in its cell. In order to allow the HNB or HeNB to perform this check, the periodic Tracking Area Update Timer Value may be sent to the HNB or HeNB through the Operations and Management (O&M) system. If no UE responds by performing the Tracking Area Update, the HNB or HeNB can assume that there is no idle state UE present in the cell. The HNB or HeNB may also perform a dummy paging for an idle state UE. If the HNB or HeNB does not receive a paging response from a UE, the HNB or HeNB can assume that there is no idle state UE present in the cell.